One of the advantages of a polygraph test is that there can be no grey areas when it comes to answering the questions.  The person undergoing the test has two simple choices: to each and every question he or she can either reply with a simple ‘yes’ or ‘no’ –with no ifs, buts or maybes.  Critics say this is one of several flaws in the test, and that there are often grey areas to questions and answers.  Nothing, they say, is rarely as black and white as yes and no. 

Defenders of the lie detector say that although the way the test is structured may be simple, the results it provides is a sophisticated way of finding out the truth. If the questions are well planned, they can be answered with straightforward yes or no answers that require no further explanation. In any case, they say, it’s the respondent’s physical reaction to the questions that is important.

What’s the background to the polygraph?

Although there had been various attempts and theories about a simple test to establish whether someone was telling the truth or not – English novelist Daniel Defoe suggested taking someone’s pulse to see if they were lying, as far back as 1730 – a Canadian is credited with inventing the modern lie detector in 1921.

Psychologist John Larson, was working with the Berkley Police in California at the time, and the test was initially meant to help reform the way police were carrying out interrogations.  The lie detector test was seen as a smarter and more reliable way of getting to the truth instead of beating it out of a suspect – a widely used tactic at the time, referred to as giving someone the ‘third degree’.

Larson developed his machine based on earlier research by fellow psychologist William Marston who monitored systolic blood pressure to see if it changed when someone was lying. Larson called his machine the polygraph – ancient Greek for ‘many writing’. The modern lie detector still measures physical reactions such as pulse, breathing and blood pressure, although the equipment used today is a software programme rather than a revolving drum of graph paper, and people taking the test are connected to a laptop.

Does it work – yes or no?

Some people swear by polygraph testing, believing it to be 98% accurate. Certainly its use and effectiveness to date has been more widely accepted in the US than in the UK. That said, a number of police forces in England have been using lie detectors to help manage convicted sex offenders since 2002 and tests are now mandatory throughout England and Wales, for the 3,000 registered sex offenders who are out on licence in the community.

If the lie detector test, as well as other information, show the offender has lied, they can be returned to prison. Offenders themselves have said that the tests helped to manage their behaviour (http://www.bbc.co.uk/news/uk-18916405).

The tests are also being more widely used in the UK by employers, who want to know if candidates have lied on their CVs, although the candidates have to agree to the tests first. Private investigators regularly use or commission polygraph tests to help them in marital infidelity cases, and others

Would I lie to you?

The now disgraced, seven-time winner of the Tour de France, Lance Armstrong, once challenged witnesses who accused him of cheating, to take a lie detector test. This was in 2012, when doping claims against him were still allegations. Since then, of course, Armstrong has admitted that he did use banned substances and has been stripped of his seven titles. Interestingly, when he said the witnesses should take a polygraph test, he stopped short of agreeing to take one himself. Subsequent events prove he had good reason to do so!